Soil samples crime

Chemistry is often used to solve crimes. Soil samples from a suspect s shoes or from the tread of the car tyre used by the suspect is analysed for pH value. This is compared with the pH of the soil at the scene of crime. The DNA (from hair, fingernail, saliva etc.) of the suspect is determined by a special technique. This is called DNA finger printing . 

The major question posed now is how can soils be used to make accurate forensic comparisons when we know that soils are highly complex and that there are thousands of different soil types in existence For example, according to the USDA, which collects soil data at many different scales, there are more than 50,000 different varieties of soil in the United States alone. Parent material, climate, organisms, and the amount of time it takes for these properties to interact will vary worldwide. First of all, soil samples must be carefully collected and handled at the crime scene and then compared by a soil scientist with forensic science experience to ensure that the soil samples can be useful during an investigation. 

Soil samples are taken from three places, a head scarf, trousers, and an area in a park at the crime scene. A portion of each sample is dried and then ground to a fine powder. Did the grinding ruin the samples ... 

The collection of physical evidence is not generally considered time sensitive however, site characterization and sampling activities are time sensitive due to the public health implications of contaminated environmental media air, water, and/or soil. Thus, collection of environmental media samples may precede collection of physical evidence, and care must be taken not to disturb the crime scene while performing these activities. If samples can be collected outside of the boundaries of the suspected crime scene, this may avoid concerns about the integrity of the crime scene. 

Soil for microbiological studies is normally collected from the plow depth (10-23 cm at Rothamsted, United Kingdom, but it may vary elsewhere) and 0-10 cm depth for grassland or forest soils. For forensic analysis the sample depth will be decided by the nature of the crime scene. However, maximum biological activity will be adjacent to a corpse and will decline with depth... 

One other type of combination is where two aspects of evidence are present in crime samples. For example, in a rape case in the United States, three flowerpots had been tipped over and spilled on the floor during the struggle. It was shown that potting soil on the suspect s shoe had a high degree of similarity with a sample collected from the floor and represented soil from... 

When someone at a crime scene comes into contact with soil, transference takes place from the soil to that person. If the soil is transferred in the commission of a crime, then this soil may be used as evidence. Interpretation of this evidence relies on, among other things, the difference in the mean measured value of the soil recovered from the suspect and a control sample... 

The first step in soil analysis is to obtain a sample composed of uniformly sized particles. This is done by sieving the gross sample obtained from the crime scene or from the possessions of the suspect. 

Forensic samples are often very small and inhomogeneous. As discussed later, it is difficult to perform quantitative analysis on such samples. However, it is possible to use qualitative XRF to good advantage. Using the spectral fingerprint of a sample does not require exact concentrations to be determined. By proving that a spectrum of soil found in a shoe matches the spectrum of soil from the location of a crime scene, it is possible to place the object at that scene. 

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